Three-dimensional memory devices having a plurality of NAND strings

ABSTRACT

Embodiments of three-dimensional (3D) memory devices and methods for forming the 3D memory devices are disclosed. In an example, a NAND memory device includes a substrate, a plurality of NAND strings on the substrate, one or more peripheral devices above the NAND strings, a single crystalline silicon layer above the peripheral devices, and one or more interconnect layers between the peripheral devices and the NAND strings. In some embodiments, the NAND memory device includes a bonding interface at which an array interconnect layer contacts a peripheral interconnect layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201710831396.8 filed on Sep. 15, 2017 and PCT Patent Application No.PCT/CN2018/077939 filed on Mar. 2, 2018 which are incorporated herein byreference in their entirety.

BACKGROUND

Embodiments of the present disclosure relate to three-dimensional (3D)memory devices and fabrication methods thereof.

Planar memory cells are scaled to smaller sizes by improving processtechnology, circuit design, programming algorithm, and fabricationprocess. However, as feature sizes of the memory cells approach a lowerlimit, planar process and fabrication techniques become challenging andcostly. As a result, memory density for planar memory cells approachesan upper limit.

A 3D memory architecture can address the density limitation in planarmemory cells. The 3D memory architecture includes a memory array andperipheral devices for controlling signals to and from the memory array.

BRIEF SUMMARY

Embodiments of 3D NAND memory architectures and fabrication methodsthereof are disclosed herein.

In some embodiments, a semiconductor apparatus includes a siliconsubstrate with a memory array (also referred to herein as an “arraydevice”) on the silicon substrate and one or more interconnect layersabove the array device. The semiconductor apparatus can also include oneor more peripheral devices above the one or more interconnect layers. Insome embodiments, the semiconductor apparatus includes a singlecrystalline silicon layer above the one or more peripheral devices. Thesemiconductor apparatus can further include a plurality ofback-end-of-line (BEOL) interconnect layers and pad layers above thesingle crystalline silicon layer.

In some embodiments, the one or more peripheral devices includes aplurality of metal-oxide-semiconductor (MOS) field-effect-transistors(FETs). In some embodiments, the peripheral devices were formed on asilicon substrate. In some embodiments, the silicon substrate includesdoped regions and isolation regions. The silicon substrate can be athinned silicon substrate, e.g., the single crystalline silicon layer.In some embodiments, the single crystalline silicon layer is part of asilicon substrate that was thinned by suitable techniques, e.g.,backside grinding, wet/dry etching, and/or chemical mechanical polishing(CMP). In some embodiments, the single crystalline silicon layer has athickness between 200 nm to 50 μm. In some embodiments, the singlecrystalline silicon layer has a thickness between 500 μm to 10 μm. Insome embodiments, the single crystalline silicon layer has a thicknessbetween 500 nm to 5 μm. In some embodiments, the single crystallinesilicon layer has a thickness less than about 1 μm. The singlecrystalline silicon layer can be partially or fully doped with n-typeand/or p-type dopants. The MOSFETs of the peripheral devices can be usedas different functional devices for the semiconductor apparatus, such aspage buffers, sense amplifiers, column decoders, and row decoders.

In some embodiments, the one or more interconnect layers include aperipheral interconnect layer, which includes a plurality of conductorlayers and contact layers. The interconnect layers can include aplurality of metal layers, in which one or more of the metal layersinclude tungsten (W), copper (Cu), aluminum (Al), or any other suitablematerials. The contact layers can also include W, Cu, Al, or any othersuitable materials. The peripheral interconnect layer can transferelectrical signals between different peripheral transistors and betweenthe peripheral device and the array device.

In some embodiments, the one or more interconnect layers also include anarray interconnect layer, which includes a plurality of conductor layersand contact layers. The conductor layers can include a plurality ofmetal layers, in which one or more of the metal layers can include W,Cu, Al, or any other suitable materials. The contact layers can alsoinclude W, Cu, Al, or any other suitable materials. The arrayinterconnect layer can transfer electrical signals between differentareas of the array device and between the peripheral device and thearray device.

In some embodiments, the array device includes a plurality of NANDstrings. A NAND string can include a semiconductor channel (e.g., asilicon channel) that extends vertically through a pluralityconductor/dielectric layer pairs. The plurality of theconductor/dielectric layer pairs are also referred to herein as a“alternating conductor/dielectric stack.” The conductor layer can beused as a word line (electrically connecting one or more control gates).Multiple layers can be formed between the conductor layer (control gate)of the alternating conductor/dielectric stack and the semiconductorchannel. In some embodiments, the multiple layers include a tunnelinglayer, such as a tunneling oxide layer, through which the electrons orholes from the semiconductor channel can tunnel to a storage layer forthe NAND string. The multiple layers can also include the storage layerto store charge. The storage or removal of charge in the storage layercan impact the on/off state and/or a conductance of the semiconductorchannel. The storage layer can include polycrystalline silicon(polysilicon) or silicon nitride. In some embodiments, the multiplelayers further include a blocking layer, such as a silicon oxide layeror a combination of silicon oxide/silicon nitride/silicon oxide (ONO)layers. In some embodiments, the blocking layer includes high dielectricconstant (high-k) dielectrics (e.g., aluminum oxide).

In some embodiments, the NAND string further includes an epitaxialsilicon layer on a lower end of the semiconductor channel. The epitaxialsilicon layer can be epitaxially grown from the silicon substrate belowthe NAND string.

In some embodiments, the NAND string further includes a select gateformed by one or more lower conductor layers of the alternatingconductor/dielectric stack. The select gate can control the on/off stateand/or a conductance of the semiconductor channel of the NAND string.The select gate of the NAND string can also be formed by a separateconductor layer below the alternating conductor/dielectric stack. Insome embodiments, the NAND string further includes another select gateformed by one or more upper conductor layers of the alternatingconductor/dielectric stack. The select gate of the NAND string can alsobe formed by a separate conductor layer above the alternatingconductor/dielectric stack.

In some embodiments, the NAND string is electrically connected to asource contact by a doped region of the silicon substrate. The dopedregion of the silicon substrate can include p-type dopants. The sourcecontact can extend vertically through the alternatingconductor/dielectric stack and can contact the doped region of thesilicon substrate at its lower end. In some embodiments, an upper end ofthe source contact is in contact with a contact above the sourcecontact.

In some embodiments, the array device further includes a plurality ofword line contacts, which extend vertically. Each word line contact caninclude an upper end in contact with a corresponding word line toindividually address the corresponding word line of the array device.The plurality of word line contacts can be contact holes and/or contacttrenches (e.g., formed by a wet etch process or a dry etch process)filled with a conductor (e.g., W). In some embodiments, the contactholes and contact trenches include a barrier layer, an adhesion layer,and/or a seed layer underneath the conductor. The contact holes and/orcontact trenches can be filled by a chemical vapor deposition (CVD)process, a physical vapor deposition (PVD) process, or an atomic layerdeposition (ALD) process.

In some embodiments, the interconnect layers above the NAND stringsinclude a plurality of bit line contacts each in contact with an upperend of a corresponding NAND string. The plurality of bit line contactscan include contact vias that are isolated from each other. Each bitline contact can be electrically connected to a corresponding NANDstring to individually address the corresponding NAND string. The bitline contacts can be contact holes and/or contact trenches (e.g., formedby a wet etch process or a dry etch process) filled with a conductor(e.g., W). The contact holes and/or contact trenches can be filled usinga CVD process, a PVD process, or an ALD process.

In some embodiments, the one or more interconnect layers furtherincludes a bonding interface between two dielectric layers, such asbetween a silicon nitride layer and a silicon oxide layer. The bondinginterface can also be between two conductor layers, such as between twometal (e.g., Cu) layers. In some embodiments, the bonding interfaceincludes both the interface between dielectric layers and the interfacebetween conductor layers. The bonding interface can be formed bychemical bonds between the dielectric layers and/or the conductor layerson both sides of the bonding interface. The bonding interface can beformed by physical interaction (e.g., inter-diffusion) between thedielectric layers and/or the conductor layers on both sides of thebonding interface. In some embodiments, the bonding interface is formedafter a plasma treatment or a thermal treatment of the surfaces fromboth sides of the bonding interface prior to the bonding process.

In some embodiments, the semiconductor apparatus further includesmultiple alternating conductor/dielectric stacks. In some embodiments,an inter-stack layer is between adjacent alternatingconductor/dielectric stacks. The inter-stack layer can electricallyconnect a NAND string from an upper alternating conductor/dielectricstack to another NAND string from a lower alternatingconductor/dielectric stack. In some embodiments, a NAND string from theupper alternating conductor/dielectric stack is electrically connectedto a NAND string from the lower alternating conductor/dielectric stackvia a conductor of the inter-stack layer, thereby creating a longer NANDstring.

In some embodiments, the semiconductor apparatus further includes one ormore through silicon contacts (TSCs) that extend vertically through thesilicon substrate with the peripheral devices. The one or more TSCs cancontact an interconnect layer (e.g., the peripheral interconnect layer)below the peripheral devices and can also contact another interconnectlayer (e.g., the BEOL interconnect layer) above the peripheral devices.The interconnect layer above the peripheral devices can include BEOLinterconnect layers and pad layers. The TSCs can include contact holesand/or trenches using dry etch processes followed by filling the contactholes and/or trenches (e.g., Ruined by a wet etch process or a dry etchprocess) with a conductor material (e.g., W, Cu, or silicides).

In some embodiments, the BEOL interconnect layers transfer electricalsignals between devices of the semiconductor apparatus, including thearray device and the peripheral device. In some embodiments, pad layersare formed to transfer electrical signals from the semiconductorapparatus to external electrical signal paths. The BEOL interconnectlayers can include interconnect conductor layers and contact layers. Theinterconnect layers and contact layers can include conductor materials,such as, W, Cu, Al, silicides, and/or any other suitable conductormaterials. The pad layer can include conductor materials, such as W, Cu,Al, silicides, or any other suitable conductor materials.

An exemplary method for fabricating a semiconductor device includesforming a peripheral device, forming an array device, and bonding theperipheral device and the array device at a bonding interface. Theexemplary method further includes forming the peripheral device,including MOS transistors, on a first silicon substrate, and forming aperipheral interconnect layer for the peripheral device.

In some embodiments, the exemplary method further includes forming dopedregions and isolation regions in a second silicon substrate, and formingone or more NAND strings on the second silicon substrate. The NANDstrings include a plurality of conductor/dielectric layer pairs, asemiconductor channel that extends vertically through the plurality ofconductor/dielectric layer pairs, a tunneling layer between thesemiconductor channel and the conductor/dielectric layer pairs, astorage layer including a plurality of storage units between thetunneling layer and the conductor/dielectric layer pairs, and a blockinglayer between the storage layer and the conductor/dielectric layerpairs. The NAND strings can contact the second silicon substrate. EachNAND string can include a select gate at an end of the NAND string.

In some embodiments, the exemplary method further includes forming anarray interconnect layer for the NAND strings. The array interconnectlayer can include bit line contacts in contact with the NAND strings.The array interconnect layer can also include one or more conductorlayers and contact layers, each of which includes conductor materials,such as W, Al, Cu, or any other suitable conductor materials.

The array interconnect layer can further include a source contact forthe NAND strings. The source contact can extend vertically through thealternating conductor/dielectric stack. The source contact can contactthe second silicon substrate on an end and can contact the arrayinterconnect layer on another end. In some embodiments, the sourcecontact is electrically connected to the NAND strings by a doped regionof the second silicon substrate.

The peripheral device can be bonded to the array device by flipping theperipheral device upside down, aligning the peripheral interconnectlayer facing down towards the array device with the array interconnectlayer facing up (in a face-to-face manner), placing the peripheraldevice above the array device so that the peripheral interconnect layeris above and in contact with the array interconnect layer, performing abonding treatment, and forming a bonding interface between the arrayinterconnect layer and the peripheral interconnect layer. In someembodiments, the bonding treatment includes a plasma process, a wetprocess, and/or a thermal process to create physical or chemical bondsbetween the array interconnect layer and the peripheral interconnectlayer at the bonding interface. In some embodiments, the arrayinterconnect layer includes a silicon nitride layer or a silicon oxidelayer, and the peripheral interconnect layer includes a silicon oxidelayer or a silicon nitride layer. In some embodiments, the conductors ofthe array interconnect layer and the peripheral interconnect layerinclude Cu.

In some embodiments, the bonding between the array interconnect layerand the peripheral interconnect layer is formed by physical interaction(e.g., inter-diffusion) between the dielectric layers (e.g., a siliconnitride layer and a silicon oxide layer) and/or the conductor layers atan interface. The interface between the array interconnect layer and theperipheral interconnect layer is referred to herein as a “bondinginterface.” In some embodiments, before the bonding process, a plasmatreatment on surfaces of the array interconnect layer and the peripheralinterconnect layer is performed to enhance the bonding strength betweenthe surfaces. Prior to the bonding process, a wet process treatment onthe surfaces of the array interconnect layer and the peripheralinterconnect layer can be performed as well to enhance the bondingstrength. In some embodiments, placement of the peripheral interconnectlayer above the array interconnect layer includes aligning contact areasof the array interconnect layer with the peripheral interconnect layerto ensure electrical contact when the two interconnect layers arebonded. In some embodiments, after the interconnect layers have madecontact with one another, a thermal treatment is performed to boostinter-diffusion between the conductor materials (e.g., Cu) from thearray interconnect layer and the peripheral interconnect layer.

In some embodiments, one or more bonding interfaces can be formed by thefabrication method. For example, multiple array devices can be bondedwith the peripheral device. In another example, the array device can bebonded with multiple peripheral devices. In still another example,multiple array devices can be bonded with multiple peripheral devices.

In some embodiments, the array device can include more than onealternating conductor/dielectric stack. Each alternatingconductor/dielectric stack can include a plurality ofconductor/dielectric layer pairs. In some embodiments, an inter-stacklayer is formed between adjacent alternating conductor/dielectricstacks. The inter-stack layer can electrically connect a NAND stringfrom an upper alternating conductor/dielectric stack with another NANDstrings from a lower alternating conductor/dielectric stack.

The exemplary method can further include, after bonding the array deviceand the peripheral device, thinning the first silicon substrate of theperipheral device. The thinning of the first silicon substrate can beperformed by a CMP process, a wet etch process, a dry etch process, orany combination thereof.

In some embodiments, the order of forming the array device/arrayinterconnect layer and the peripheral device/peripheral interconnectlayer can be modified, or the fabrication of the array device/arrayinterconnect layer and the fabrication of the peripheraldevice/peripheral interconnect layer can be performed in parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosureand, together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1 illustrates a cross-section of an exemplary 3D memory device.

FIG. 2 illustrates a cross-section of a 3D memory device, according tosome embodiments.

FIGS. 3A-3D illustrate an exemplary fabrication process for forming aperipheral device and a peripheral interconnect layer, according to someembodiments.

FIGS. 4A-4D illustrate an exemplary fabrication process for forming anarray device and an array interconnect layer, according to someembodiments.

FIGS. 5A-5C illustrate an exemplary fabrication process for forming a 3Dmemory device with an array device bonded to a peripheral device,according to some embodiments.

FIG. 6 is a flowchart of an exemplary method for forming a peripheraldevice and a peripheral interconnect layer, according to someembodiments.

FIG. 7 is a flowchart of an exemplary method for foil ling an arraydevice and an array interconnect layer, according to some embodiments.

FIG. 8 is a flowchart of an exemplary method for joining a peripheraldevice and an array device, according to some embodiments.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to effect such feature, structure orcharacteristic in connection with other embodiments whether or notexplicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The semiconductor apparatus can be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure, or can have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which contacts, interconnect lines, and/or vias are formed) and oneor more dielectric layers.

As used herein, the term “nominal/nominally” refers to a desired, ortarget, value of a characteristic or parameter for a component or aprocess operation, set during the design phase of a product or aprocess, together with a range of values above and/or below the desiredvalue. The range of values can be due to slight variations inmanufacturing processes or tolerances. As used herein, the term “about”indicates the value of a given quantity that can vary based on aparticular technology node associated with the subject semiconductordevice. Based on the particular technology node, the term “about” canindicate a value of a given quantity that varies within, for example,10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

As used herein, the term “3D memory device” refers to a semiconductordevice with vertically oriented strings of memory cell transistors(referred to herein as “memory strings,” such as NAND strings) on alaterally oriented substrate so that the memory strings extend in thevertical direction with respect to the substrate. As used herein, theterm “vertical/vertically” means nominally perpendicular to the lateralsurface of a substrate.

Various embodiments in accordance with the present disclosure provide a3D memory device with smaller die size, higher device density, andimproved performance compared with other 3D memory devices. Byvertically stacking a peripheral device and BEOL interconnect above anarray device, the density of 3D memory devices can be increased.Moreover, by decoupling the peripheral device processing and the arraydevice processing, the thermal budget associated with processing thearray device is not limited by the peripheral device performancerequirement; similarly, the peripheral device performance is notimpacted by the array device processing. For example, the peripheraldevice and the array device can be separately fabricated on differentsubstrates so that certain high-temperature processes for fabricatingthe array device will not adversely affect the fabrication of theperipheral device (e.g., avoid excess diffusion of the dopants, controlthe doping concentration and/or thickness of ion implantation, etc.).

FIG. 1 illustrates a cross-section of an exemplary 3D memory device 100.3D memory device 100 includes a substrate 102 and peripheral devices onsubstrate 102. An interconnect layer 104 for the peripheral devices isformed above substrate 102. A memory array structure 106 is formed aboveinterconnect layer 104.

3D memory device 100 represents an example of a monolithic 3D memorydevice. The term “monolithic” means that the components of the 3D memorydevice are formed on a single substrate. For monolithic 3D memorydevices, the fabrication encounters additional restrictions due to theconvolution of the peripheral device processing and the memory arrayprocessing. For example, the fabrication of memory array structure(e.g., NAND strings) is constrained by the thermal budget associatedwith the peripheral devices that have been formed or to be formed on thesame substrate. In contrast, as described in detail in the presentdisclosure, components of a 3D memory device (e.g., peripheral devicesand memory array structures) can be formed separately on differentsubstrates and then joined to form a non-monolithic 3D memory device.The de-convolution of the peripheral device processing and memory arrayprocessing from each other can improve the performance of the resulting3D memory device.

FIG. 2 illustrates a cross-section of an exemplary 3D memory device 200according to some embodiments of the present disclosure. 3D memorydevice 200 can include a substrate 202, which can include silicon (e.g.,single crystalline silicon), silicon germanium (SiGe), gallium arsenide(GaAs), germanium (Ge), silicon on insulator (SOI), or any othersuitable materials.

3D memory device 200 can include a memory array device above substrate202. It is noted that x and y axes are added in FIG. 2 to furtherillustrate the spatial relationship of the components in 3D memorydevice 200. Substrate 202 includes two lateral surfaces (e.g., a topsurface and a bottom surface) extending laterally in the x-direction(the lateral direction or width direction). As used herein, whether onecomponent (e.g., a layer or a device) is “on,” “above,” or “below”another component (e.g., a layer or a device) of a semiconductor device(e.g., 3D memory device 200) is determined relative to the substrate ofthe semiconductor device (e.g., substrate 202) in the y-direction (thevertical direction or thickness direction) when the substrate ispositioned in the lowest plane of the semiconductor device in they-direction. The same notion for describing spatial relationship isapplied throughout the present disclosure.

As shown in FIG. 2, 3D memory device 200 is a NAND Flash memory devicein which memory cells are provided in the form of a plurality of NANDstrings 230 extending vertically above substrate 202. The array devicecan include a plurality of NAND strings 230 that extends through aplurality of conductor layer 234 and dielectric layer 236 pairs 242. Theplurality of conductor/dielectric layer pairs 242 are also referred toherein as an “alternating conductor/dielectric stack.” Conductor layers234 and dielectric layers 236 in alternating conductor/dielectric stack242 alternate in the vertical direction. In other words, except the onesat the top or bottom of alternating conductor/dielectric stack 242, eachconductor layer 234 can be adjoined by two dielectric layers 236 on bothsides, and each dielectric layer 236 can be adjoined by two conductorlayers 234 on both sides. Conductor layers 234 can have the samethickness or can have different thicknesses. Similarly, dielectriclayers 236 can each have the same thickness or can have differentthicknesses. In some embodiments, alternating conductor/dielectric stack242 can include more conductor layers or more dielectric layers withdifferent materials and/or thicknesses than the conductor/dielectriclayer pair. Conductor layer 234 can include conductor materials, such astungsten (W), cobalt (Co), copper (Cu), aluminum (Al), doped silicon,silicides, any other suitable conductor materials, or any combinationthereof. Dielectric layer 236 can include dielectric materials, such assilicon oxide, silicon nitride, silicon oxynitride, any other suitabledielectric materials, or any combination thereof.

As shown in FIG. 2, each NAND string 230 can include a semiconductorchannel 228 and a dielectric layer 229 (also known as “memory film”). Insome embodiments, semiconductor channel 228 includes silicon, such asamorphous silicon, polysilicon, or single crystalline silicon. In someembodiments, dielectric layer 229 is a composite layer including atunneling layer, a storage layer (also known as “charge trap/storagelayer”), and a blocking layer. Each NAND string 230 can have a cylindershape (e.g., a pillar shape). Semiconductor channel 228, the tunnelinglayer, the storage layer, and the blocking layer are arranged along adirection from the center toward the outer surface of the pillar in thisorder, according to some embodiments. The tunneling layer can includesilicon oxide, silicon nitride, or any combination thereof. The blockinglayer can include silicon oxide, silicon nitride, high dielectricconstant (high-k) dielectrics, or any combination thereof. The storagelayer can include silicon nitride, silicon oxynitride, silicon, or anycombination thereof. In some embodiments, dielectric layer 229 caninclude ONO dielectrics (e.g., a tunneling layer including siliconoxide, a storage layer including silicon nitride, and a blocking layerincluding silicon oxide).

In some embodiments, NAND strings 230 further include a plurality ofcontrol gates (each being part of a word line) for NAND strings 230.Each conductor layer 234 in alternating conductor/dielectric stack 242can act as a control gate for each memory cell of NAND string 230. Asshown in FIG. 2, NAND strings 230 can include a select gate 238 (e.g., asource select gate) at a lower end of NAND string 230. NAND strings 230can also include another select gate 240 (e.g., a drain select gate) atan upper end of the NAND string 230. As used herein, the “upper end” ofa component (e.g., NAND string 230) is the end further away fromsubstrate 202 in the y-direction, and the “lower end” of the component(e.g., NAND string 230) is the end closer to substrate 202 in they-direction. As shown in FIG. 2, for each NAND string 230, source selectgate 238 can be below drain select gate 240. In some embodiments, selectgates 238 and 240 include conductor materials including, but not limitedto, W, Co, Cu, Al, doped silicon, silicides, or any combination thereof.

In some embodiments, 3D memory device 200 includes an epitaxial layer251 on a lower end of semiconductor channel 228 of NAND string 230.Epitaxial layer 251 can include a semiconductor material, such assilicon. Epitaxial layer 251 can be epitaxially grown from substrate202. For example, substrate 202 can be a silicon substrate, andepitaxial layer 251 can be a single crystalline silicon layerepitaxially grown from the silicon substrate. Substrate 202 can beundoped, partially doped (in the thickness direction and/or the widthdirection), or fully doped by p-type or n-type dopants. For each NANDstring 230, epitaxial layer 251 is referred to herein as an “epitaxialplug.” Epitaxial plug 251 at the lower end of each NAND string 230 cancontact both semiconductor channel 228 and a doped region 250 ofsubstrate 202. Epitaxial plug 251 can function as the channel controlledby select gate 238 at the lower end of NAND string 230.

In some embodiments, the array device further includes a source contact232 that extends vertically through alternating conductor/dielectricstack 242. As shown in FIG. 2, a lower end of source contact 232 cancontact doped region 250 of substrate 202 (e.g., an array common sourcefor NAND strings 230). In some embodiments, source contact 232 includesconductor materials including, but not limited to, W, Co, Cu, Al,silicides, or any combination thereof. In some embodiments, substrate202 includes an isolation region 246. In some embodiments, isolationregion 246 can form across the entire thickness of substrate 202.

In some embodiments, the array device further includes one or more wordline contacts 258 in a staircase structure region. Word line contacts258 can extend vertically within a dielectric layer 259. Each word linecontact 258 can have an end (e.g., the lower end) in contact with acorresponding conductor layer 234 in alternating conductor/dielectricstack 242 to individually address a corresponding word line of the arraydevice. In some embodiments, each word line contact 258 is above acorresponding word line 234. Word line contacts 258 can be contact holesand/or contact trenches (e.g., formed by a wet etch process or a dryetch process) filled with a conductor (e.g., W). In some embodiments,filling the contact holes and/or contact trenches includes depositing abarrier layer, an adhesion layer, and/or a seed layer before depositingthe conductor.

In some embodiments, source contact 232 and NAND strings 230 are both incontact with doped region 250 of substrate 202, so that source contact232 can be electrically connected to NAND strings 230 when doped region250 conducts an electrical signals (e.g., when an inversion layer insubstrate 202 forms for conduction.)

As shown in FIG. 2, 3D memory device 200 can include an arrayinterconnect layer 223 above the array device and in contact with aperipheral interconnect layer 222. Array interconnect layer 223 caninclude bit line contacts 226, word line vias 257, one or more conductorlayers (e.g., a conductor layer 224), and one or more dielectric layers(e.g., dielectric layers 221 and 225). The conductor layers can includeconductor materials including, but not limited to, W, Co, Cu, Al,silicides, or any combination thereof. The dielectric layers can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, low-k dielectrics, or any combination thereof.

As shown in FIG. 2, each bit line contact 226 can contact the upper endof a corresponding NAND string 230 to individually address correspondingNAND string 230. Each word line via 257 can contact the upper end of acorresponding word line contact 258 to individually address acorresponding word line 234 of NAND strings 230.

3D memory device 200 can include a peripheral device (e.g., transistors206) and a semiconductor layer 244 (e.g., a thinned substrate) above theperipheral device. The entirety or part of the peripheral device can beformed in semiconductor layer 244 (e.g., above the bottom surface ofsemiconductor layer 244) and/or directly below semiconductor layer 244.The peripheral device can include a plurality of transistors 206.Semiconductor layer 244 can be a thinned substrate on which theperipheral device (e.g., transistors 206) is formed. In someembodiments, semiconductor layer 244 includes a single crystallinesilicon, in which semiconductor layer 244 can be referred to as a“single crystalline silicon layer.” In some embodiments, semiconductorlayer 244 can include SiGe, GaAs, Ge, or any other suitable materials.An isolation region 204 and a doped region 208 (e.g., a source region ora drain region of transistor 206) can be formed in semiconductor layer244 as well.

In some embodiments, the peripheral device can include any suitabledigital, analog, and/or mixed-signal peripheral circuits used forfacilitating the operation of 3D memory device 200. For example, theperipheral device can include one or more of a page buffer, a decoder(e.g., a row decoder and a column decoder), a sense amplifier, a driver,a charge pump, a current or voltage reference, or any active or passivecomponents of the circuits (e.g., transistors, diodes, resistors, orcapacitors).

3D memory device 200 can include peripheral interconnect layer 222 belowtransistors 206 to transfer electrical signals to and from transistors206. Peripheral interconnect layer 222 can include one or more contacts,such as a contact 207 and a contact 214, and one or more interconnectconductor layers, such as a conductor layer 216 and a conductor layer220, each including one or more interconnect lines and/or vias. As usedherein, the term “contact” can broadly include any suitable types ofinterconnects, such as middle-end-of-line (MEOL) interconnects andback-end-of-line (BEOL) interconnects, including vertical interconnectaccesses (e.g., vias) and lateral lines (e.g., interconnect lines).Peripheral interconnect layer 222 can further include one or moreinterlayer dielectric (ILD) layers, such as dielectric layers 210, 212,and 218. That is, peripheral interconnect layer 222 can includeconductor layers 216 and 220 and dielectric layers 210, 212, and 218.The contacts and the conductor layers in peripheral interconnect layer222 can include conductor materials including, but not limited to, W,Co, Cu, Al, silicides, or any combination thereof. The dielectric layersin peripheral interconnect layer 222 can include dielectric materialsincluding, but not limited to, silicon oxide, silicon nitride, siliconoxynitride, doped silicon oxide, or any combination thereof.

A bonding interface 219 can be formed between dielectric layer 218 ofperipheral interconnect layer 222 and dielectric layer 221 of arrayinterconnect layer 223. Bonding interface 219 can also be formed betweenconductor layer 224 of array interconnect layer 223 and conductor layer220 of peripheral interconnect layer 222. Each of dielectric layer 218and dielectric layer 221 can include silicon nitride, or silicon oxide.

In some embodiments, a first semiconductor structure 260 is bonded to asecond semiconductor structure 262 at bonding interface 219. Firstsemiconductor structure 260 can include substrate 202, arrayinterconnect layer 223, alternating conductor/dielectric stack 242having a plurality of conductor/dielectric layer pairs, and NAND strings230. Second semiconductor structure 262 can include semiconductor layer244 (e.g., a thinned substrate), one or more peripheral devices belowsemiconductor layer 244, and peripheral interconnect layer 222 below theone or more peripheral devices. First semiconductor structure 260 caninclude the elements shown below bonding interface 219 in FIG. 2, whilesecond semiconductor structure 262 can include the elements shown abovebonding interface 219 in FIG. 2. Peripheral interconnect layer 222 caninclude conductor layer 220, which contacts conductor layer 224 of arrayinterconnect layer 223 at bonding interface 219. Peripheral interconnectlayer 222 can also include dielectric layer 218, which contactsdielectric layer 221 of array interconnect layer 223 at bondinginterface 219.

As shown in FIG. 2, 3D memory device 200 can include one or more throughsilicon contacts (TSCs) 211 that extend vertically through semiconductorlayer 244. The lower end of TSC 211 can be in contact with a conductorlayer of peripheral interconnect layer 222 (e.g., conductor layer 216).The upper end of TSC 211 can be in contact with a BEOL conductor layer248 and/or pad layers 256 above semiconductor layer 244. TSC 211 can beformed in an isolation region that extends through the entire thicknessof semiconductor layer 244, so that TSC 211 can be electrically isolatedfrom other parts of semiconductor layer 244 (e.g., doped regions 208).In some embodiments, TSC 211 carries electrical signals from the one ormore peripheral devices to BEOL conductor layer 248 and/or pad layer256. In some embodiments, TSC 211 can include a vertical opening (e.g.,a contact hole or a contact trench) through semiconductor layer 244formed by dry/wet etch process, followed by filling the opening withconductor materials and other materials (e.g., dielectric material) forisolation purposes. TSC 211 can include conductor materials including,but not limited to, W, Co, Cu, Al, doped silicon, silicides, or anycombination thereof. Dielectric materials can be deposited in theopening prior to the filling of conductor materials. Dielectricmaterials can include, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, doped silicon oxide, or any combinationthereof.

As shown in FIG. 2, 3D memory device 200 can further include a BEOLinterconnect layer 253 above semiconductor layer 244. In someembodiments, BEOL interconnect layer 253 includes conductor layer 248,one or more dielectric layers (e.g., a dielectric layer 252), and one ormore pad layers (e.g., pad layer 256). BEOL interconnect layer 253 cantransfer electrical signals between 3D memory device 200 and externalcircuits. The conductor layers, contact layers, and pad layers in BEOLinterconnect layer 253 can include conductor materials, such as W, Co,Cu, Al, silicides, any other suitable conductor material, or anycombination thereof. The dielectric layers in BEOL interconnect layer253 can include dielectric materials, such as silicon oxide, siliconnitride, low-k dielectrics, any other suitable dielectric material, orany combination thereof.

BEOL interconnect layer 253 can be electrically connected to the one ormore peripheral devices. Specifically, TSC 211 can extend verticallythrough semiconductor layer 244, dielectric layer 210, and at least partof dielectric layer 252. TSC 211 can contact a conductor layer of BEOLinterconnect layer 253 (e.g., conductor layer 248) and a conductor layerof peripheral interconnect layer 222 (e.g., conductor layer 216).

FIG. 3A to FIG. 3D illustrate an exemplary fabrication process forforming a peripheral device and a peripheral interconnect layer. FIG. 6is a flowchart of an exemplary method 600 for forming a peripheraldevice and a peripheral interconnect layer. An example of the peripheraldevice and peripheral interconnect layer depicted in FIGS. 3A-3D andFIG. 6 is the peripheral device (e.g., transistors 206) and peripheralinterconnect layer 222 depicted in FIG. 2. It should be understood thatthe operations shown in method 600 are not exhaustive and that otheroperations can be performed as well before, after, or between any of theillustrated operations.

Referring to FIG. 6, method 600 starts at operation 602, in which aperipheral device is formed on a first substrate. The first substratecan be a silicon substrate. As illustrated in FIG. 3A, a peripheraldevice is formed on a first silicon substrate 302. The peripheral devicecan include a plurality of transistors 304 formed on first siliconsubstrate 302. Transistors 304 can be formed by a plurality ofprocessing steps including, but not limited to, photolithography,dry/wet etch, thin film deposition, thermal growth, implantation, CMP,or any combination thereof. In some embodiments, doped regions 305 areformed in first silicon substrate 302. In some embodiments, an isolationregion 306 is also formed in first silicon substrate 302.

Method 600 proceeds to operation 604, as illustrated in FIG. 6, in whichone or more dielectric layers and conductor layers are formed above theperipheral device. As illustrated in FIG. 3B, a first dielectric layer310 can be formed on first silicon substrate 302. First dielectric layer310 can include a contact layer 308, including MEOL contacts, to makeelectrical connections with the peripheral device (e.g., transistors304).

As illustrated in FIG. 3C, a second dielectric layer 316 is formed onfirst dielectric layer 310. In some embodiments, second dielectric layer316 is a combination of multiple layers and can be formed in separatesteps. For example, second dielectric layer 316 can include a conductorlayer 312 and a contact layer 314. The conductor layers (e.g., conductorlayer 312) and contact layers (e.g., contact layers 308 and 314) caninclude conductor materials deposited by one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD,electroplating, electroless plating, or any combination thereof.Fabrication processes for forming the conductor layers and contactlayers can also include photolithography, CMP, wet/dry etch, or anycombination thereof. The dielectric layers can be formed by thin filmdeposition processes including, but not limited to, CVD, PVD, ALD, orany combination thereof.

Method 600 proceeds to operation 606, as illustrated in FIG. 6, in whicha top dielectric layer and a top conductor layer of a peripheralinterconnect layer are formed. The dielectric layers and conductorlayers formed at operations 604 and 606 can be collectively referred toas an “interconnect layer” (e.g., the peripheral interconnect layer).Each of the dielectric layers and conductor layers can be a portion ofthe peripheral interconnect layer that transfers electrical signals toand from the peripheral device. As illustrated in FIG. 3D, a thirddielectric layer (the top dielectric layer) 318 is formed on seconddielectric layer 316, and a top conductor layer 320 is formed in thirddielectric layer 318. As a result, a peripheral interconnect layer 322is formed. The conductor layer (e.g., conductor layer 320) can includeconductor materials deposited by one or more thin film depositionprocesses including, but not limited to, CVD, PVD, ALD, electroplating,electroless plating, or any combination thereof. Fabrication processesto form the conductor layer and contact layers can also includephotolithography, CMP, wet/dry etch, or any combination thereof. Thedielectric layers (e.g., dielectric layer 318) can include dielectriclayers deposited by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, or any combinationthereof.

FIG. 4A to FIG. 4D illustrate an exemplary fabrication process forforming an array device and an array interconnect layer. FIG. 7 is aflowchart of an exemplary method 700 for forming an array device and anarray interconnect layer. An example of the array device and arrayinterconnect layer depicted in FIGS. 4A-4D and FIG. 7 is the arraydevice (e.g., NAND strings 230) and array interconnect layer 223depicted in FIG. 2. It should be understood that the operations shown inmethod 700 are not exhaustive and that other operations can be performedas well before, after, or between any of the illustrated operations.

Referring to FIG. 7, method 700 starts at operation 702, in which adoped region and an isolation region are formed in a second substrate.The second substrate can be a silicon substrate, such as a secondsilicon substrate 402 in FIG. 4A. An array device can be formed onsecond silicon substrate 402. In some embodiments, a doped region 404and an isolation region 406 are formed in second silicon substrate 402.Doped region 404 can be formed by ion implantation and/or diffusion.Isolation region 406 can be formed by thermal growth and/or thin filmdeposition. Patterning process (e.g., photolithography and dry/wet etch)can be used for patterning doped region 404 and isolation region 406 insecond silicon substrate 402.

Method 700 proceeds to operation 704, as illustrated in FIG. 7, in whicha plurality of dielectric layer pairs (also referred to herein as an“alternating dielectric stack”) are formed on the second substrate. Asillustrated in FIG. 4B, a plurality of dielectric layer 410 anddielectric layer 412 layer pairs are formed on second silicon substrate402. The plurality of dielectric pairs can form an alternatingdielectric stack 408. Alternating dielectric stack 408 can include analternating stack of a first dielectric layer 410 and a seconddielectric layer 412 that is different from first dielectric layer 410.In some embodiments, each dielectric layer pair includes a layer ofsilicon nitride and a layer of silicon oxide. In some embodiments, thereare more layers than the dielectric layer pairs made of differentmaterials and with different thicknesses in alternating dielectric stack408. Alternating dielectric stack 408 an be formed by one or more thinfilm deposition processes including, but not limited to, CVD, PVD, ALD,or any combination thereof. In some embodiments, alternating dielectricstack 408 can be replaced by a plurality of conductor/dielectric layerpairs, i.e., an alternating stack of a conductor layer (e.g.,polysilicon) and a dielectric layer (e.g., silicon oxide).

Method 700 proceeds to operation 706, as illustrated in FIG. 7, in whicha plurality of NAND strings of the array device are formed on the secondsubstrate. As illustrated by in FIG. 4C, a plurality of NAND strings 418are formed on second silicon substrate 402. Each first dielectric layer410 of alternating dielectric stack 408 can be replaced by a conductorlayer 416, thereby forming a plurality of conductor/dielectric layerpairs in an alternating conductor/dielectric stack 414. The replacementof first dielectric layers 410 with conductor layers 416 can beperformed by wet etching first dielectric layers 410 selective to seconddielectric layers 412 and filling the structure with conductor layers416. Conductor layers 416 can be filled by CVD, ALD, any other suitableprocess, or any combination thereof. Conductor layers 416 can includeconductor materials including, but not limited to, W, Co, Cu, Al,polysilicon, silicides, or any combination thereof.

In some embodiments, fabrication processes to form NAND strings 418further include forming a semiconductor channel 420 that extendsvertically through alternating conductor/dielectric stack 414. In someembodiments, fabrication processes to form NAND strings 418 furtherinclude forming a dielectric layer 422 between semiconductor channel 420and the plurality of conductor/dielectric layer pairs in alternatingconductor/dielectric stack 414. Dielectric layer 422 can be a compositedielectric layer including, but not limited to, a tunneling layer, astorage layer, and a blocking layer. The tunneling layer can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, silicon oxynitride, or any combination thereof. Thestorage layer can include materials for storing charge for memoryoperation. The storage layer materials include, but are not limited to,silicon nitride, silicon oxynitride, a combination of silicon oxide andsilicon nitride, or any combination thereof. The blocking layer caninclude dielectric materials including, but not limited to, siliconoxide or a combination of silicon oxide/silicon nitride/silicon oxide(ONO). The blocking layer can further include a high-k dielectric layer(e.g., aluminum oxide). Dielectric layer 422 can be formed by processessuch as ALD, CVD, PVD, any other suitable processes, or any combinationthereof.

In some embodiments, fabrication processes to form NAND strings 418further include forming an epitaxial layer 426 at an end of NAND string418. As illustrated in FIG. 4C, epitaxial layer 426 can be formed at alower end of each NAND string 418 as an epitaxial plug 426. Epitaxiallayer 426 can be a silicon layer epitaxially grown from second siliconsubstrate 402 and can be implanted to a desired doping level.

In some embodiments, operation 706 further includes forming one or moresource contacts. As illustrated in FIG. 4C, a source contact 424 thatextends vertically through alternating conductor/dielectric stack 414can be formed on second silicon substrate 402. Source contact 424 canhave an end in contact with doped region 404 of second silicon substrate402. In some embodiments, source contact 424 is electrically connectedto NAND strings 418 by doped region 404 of second silicon substrate 402.A select gate 428 can be formed at an end of NAND string 418 to turn onor turn off doped region 404 of second silicon substrate 402 and controla conduction between source contact 424 and NAND strings 418. Sourcecontact 424 can include conductor materials including, but not limitedto, W, Co, Cu, Al, doped silicon, silicides, or any combination thereof.Source contact 424 can be formed by a dry/wet etch process to form avertical opening through alternating conductor/dielectric stack 414,followed by a fill process to fill the opening with conductor materialsand other materials (e.g., dielectric materials). The opening can befilled by ALD, CVD, PVD, electroplating, any other suitable processes,or any combination thereof.

In some embodiments, operation 706 further includes forming one or moreword line contacts. As illustrated in FIG. 4C, word line contacts 425are formed on second silicon substrate 402. Each word line contact 425can extend vertically through a dielectric layer 423. In someembodiments, an end of word line contact 425 lands on a word line ofNAND strings 418 (e.g., a conductor layer 416), such that each word linecontact 425 is electrically connected to a corresponding conductor layer416. Each word line contact 425 can be electrically connected to acorresponding conductor layer 416 to individually address acorresponding word line of NAND strings 418. One or more word linecontacts 425 can further contact second silicon substrate 402 or aselect gate of NAND string 418 (e.g., source select gate 428 or drainselect gate 430).

In some embodiments, fabrication processes to form word line contacts425 include forming a vertical opening through dielectric layer 423using dry/wet etch process, followed by filling the opening withconductor materials and other materials (e.g., a barrier layer, anadhesion layer, and/or a seed layer) for conductor filling, adhesion,and/or other purposes. Word line contacts 425 can include conductormaterials including, but not limited to, W, Co, Cu, Al, doped silicon,silicides, or any combination thereof. The openings of word linecontacts 425 can be filled with conductor materials and other materialsby ALD, CVD, PVD, electroplating, any other suitable processes, or anycombination thereof.

Method 700 proceeds to operation 708, as illustrated in FIG. 7, in whichan array interconnect layer is formed above the plurality of NANDstrings. The array interconnect layer can transfer electrical signalsbetween the NAND strings and other parts of the 3D memory devices, suchas the peripheral device. As illustrated in FIG. 4D, an arrayinterconnect layer 438 is formed above NAND strings 418. In someembodiments, fabrication processes to form array interconnect layer 438include forming a dielectric layer 434, followed by forming a pluralityof bit line contacts 432 in contact with NAND strings 418 in dielectriclayer 434. Dielectric layer 434 can include one or more layers ofdielectric materials such as silicon oxide, silicon nitride, siliconoxynitride, or any combination thereof. Bit line contacts 432 can beformed by forming openings in dielectric layer 434, followed by fillingthe openings with conductor materials and dielectric materials. Bit linecontacts 432 can include conductor materials including, but not limitedto, W, Co, Cu, Al, doped silicon, silicides, or any combination thereof.The openings of bit line contacts 432 can be filled with conductormaterials and dielectric materials by ALD, CVD, PVD, any other suitableprocesses, or any combination thereof.

In some embodiments, fabrication processes to form array interconnectlayer 438 further include forming a plurality of word line vias 437 indielectric layer 434. Each word line via 437 can contact an end of acorresponding word line contact 425 to enable electrical connections.Word line vias 437 can be formed by forming openings in dielectric layer434, followed by filling the openings with conductor materials. Othermaterials, such as barrier materials and/or seed layer materials, canalso be used to partially fill the openings before filling the conductormaterials to enhance the adhesion or filling performance of theconductor materials. Word line vias 437 can include conductor materialsincluding, but not limited to, W, Co, Cu, Al, doped silicon, silicides,or any combination thereof. The openings of word line vias 437 can befilled with conductor materials and barrier materials by ALD, CVD, PVD,electroplating, any other suitable processes, or any combinationthereof.

In some embodiments, fabrication process to form array interconnectlayer 438 further include forming one or more conductor layers (e.g.,conductor layer 440) and one or more contact layers 444 in dielectriclayer 434. Conductor layer 440 and contact layer 444 can includeconductor materials including, but not limited to, W, Co, Cu, Al, dopedsilicon, silicides, or any combination thereof. Conductor layers 440 andconductor contact layers 444 can be formed by any suitable known BEOLmethods.

In some embodiments, fabrication processes to form array interconnectlayer 438 further include forming a top conductor layer 442 and a topdielectric layer 436. Top conductor layer 442 can include conductormaterials including, but not limited to, W, Co, Cu, Al, doped silicon,silicides, or any combination thereof. Dielectric layer 436 can includedielectric materials including, but not limited to, silicon oxide,silicon nitride, silicon oxynitride, or any combination thereof.

FIG. 5A to FIG. 5C illustrate an exemplary fabrication process forforming a 3D memory device with an array device bonded with a peripheraldevice. FIG. 8 is a flowchart for an exemplary method 800 of joining thearray device and the peripheral device. An example of the 3D memorydevice depicted in FIGS. 5A-5C and FIG. 8 is 3D memory device 200described in FIG. 2. It should be understood that the operations shownin method 800 are not exhaustive and that other operations can beperformed as well before, after, or between any of the illustratedoperations.

Referring to FIG. 8, method 800 starts at operation 802, in which theperipheral device (and the peripheral interconnect layer) is positionedbelow the first substrate (e.g., by flipping the first substrate upsidedown) and the peripheral interconnect layer is aligned with the arrayinterconnect layer. As illustrated in FIG. 5A, peripheral interconnectlayer 322 can be placed below first silicon substrate 302. In someembodiments, aligning array interconnect layer 438 with peripheralinterconnect layer 322 is performed by aligning conductor layer 442 ofarray interconnect layer 438 with conductor layer 320 of peripheralinterconnect layer 322. As a result, conductor layer 442 can contactconductor layer 320 when the peripheral device is joined with the arraydevice.

Method 800 proceeds to operation 804, as illustrated in FIG. 8, in whichthe array interconnect layer is joined with the peripheral interconnectlayer. The array interconnect layer can be joined with the peripheralinterconnect layer by flip-chip bonding the first and second substrates.In some embodiments, the array interconnect layer and the peripheralinterconnect layer are joined by hybrid bonding of the first substrateand the second substrate in a face-to-face manner, such that theperipheral interconnect layer is above and in contact with the arrayinterconnect layer in the resulting 3D memory device. Hybrid bonding(also known as “metal/dielectric hybrid bonding”) can be a directbonding technology (e.g., forming bonding between surfaces without usingintermediate layers, such as solder or adhesives), which obtainsmetal-metal bonding and dielectric-dielectric bonding simultaneously. Asillustrated in FIG. 5B, array interconnect layer 438 can be joined withperipheral interconnect layer 322, thereby forming a bonding interface503.

As illustrated in FIG. 5A, a treatment process 502 can be used toenhance the bonding strength between array interconnect layer 438 andperipheral interconnect layer 322 before or during the joining processof the two interconnect layers. In some embodiments, each of dielectriclayer 436 and dielectric layer 318 include silicon oxide or siliconnitride. In some embodiments, treatment process 502 includes a plasmatreatment that treats the surfaces of array interconnect layer 438 andperipheral interconnect layer 322 so that the surfaces of the twointerconnect layers form chemical bonds between dielectric layer 436 anddielectric layer 318. In some embodiments, treatment process 502includes a wet process that treats the surfaces of array interconnectlayer 438 and peripheral interconnect layer 322 so that the surfaces ofthe two interconnect layers form preferable chemical bonds to enhancethe bonding strength between two dielectric layers 436 and 318.

In some embodiments, treatment process 502 includes a thermal processthat can be performed at a temperature from about 250° C. to about 600°C. (e.g., from 250° C. to 600° C.). The thermal process can causeinter-diffusion between conductor layer 442 and conductor layer 320. Asa result, conductor layer 442 can be inter-mixed with conductor layer320 after the joining process. Conductor layer 442 and conductor layer320 can each include Cu.

Method 800 proceeds to operation 806, as illustrated in FIG. 8, in whichthe first substrate is thinned, so that the thinned first substrateserves as a semiconductor layer above the peripheral devices. Asillustrated in FIG. 5B, the thinned first silicon substrate 302 can be asingle crystalline silicon layer 504. In some embodiments, after thethinning process, single crystalline silicon layer 504 has a thicknessbetween about 200 nm and about 5 μm, such as between 200 nm and 5 μm(e.g., 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1μm, 2 μm, 3 μm, 4 μm, 5 μm, any range bounded on the lower end by any ofthese values, or in any range defined by any two of these values). Insome embodiments, single crystalline silicon layer 504 has a thicknessbetween about 150 nm and about 50 μm, such as between 150 nm and 50 μm(e.g., 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 1 μm, 5 μm, 10 μm, 15 μm,20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, any range bounded onthe lower end by any of these values, or in any range defined by any twoof these values). In some embodiments, single crystalline silicon layer504 has a thickness between about 500 nm and about 10 μm, such asbetween 500 nm and 10 μm (e.g., 500 nm, 600 nm, 700 nm, 800 nm, 900 nm,1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, any rangebounded on the lower end by any of these values, or in any range definedby any two of these values). In some embodiments, single crystallinesilicon layer 504 has a thickness less than about 1 μm, such as lessthan 1 μm (e.g., 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm,70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600nm, 700 nm, 800 nm, 900 nm, any range bounded on the lower end by any ofthese values, or in any range defined by any two of these values). Firstsubstrate 302 can be thinned by processes, such as wafer grinding, dryetch, wet etch, CMP, any other suitable process, or any combinationthereof.

Method 800 proceeds to operation 808, as illustrated in FIG. 8, in whicha BEOL interconnect layer is formed above the semiconductor layer. Asillustrated in FIG. 5C, a BEOL interconnect layer 505 is formed abovesingle crystalline silicon layer 504. BEOL interconnect layer 505 caninclude a dielectric layer 506, one or more contact layers 508, one ormore conductor layers 510, and one or more pad layers 512. Dielectriclayer 506 can be a combination of multiple dielectric layers formed atseparate process steps. Contact layer 508, conductor layer 510, and padlayer 512 can include conductor materials, such as W, Co, Cu, Al, dopedsilicon, silicides, any other suitable conductor material, or anycombination thereof. Dielectric layer 506 can include dielectricmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, any other dielectric material, or any combinationthereof. In some embodiments, pad layer 512 is electrically connected toexternal circuits or devices to transfer electrical signals between thejoined array/peripheral device and the external circuits or devices.

As illustrated in FIG. 5C, a TSC 514 can be formed through singlecrystalline silicon layer 504 to make electrical contact between aconductor layer of peripheral interconnect layer 322 and a conductorlayer of BEOL interconnect layer 505. In some embodiments, TSC 514extends through an isolation region 516 formed in single crystallinesilicon layer 504, so that the lower end of TSC 514 can contactperipheral interconnect layer 322 (e.g., conductor layer 312). In someembodiments, fabrication processes for forming TSC 514 further includeforming isolation region 516 between TSC 514 and single crystallinesilicon layer 504.

Various embodiments in accordance with the present disclosure provide a3D memory device with smaller die size, higher device density, andimproved performance compared with other 3D memory devices. Byvertically stacking a peripheral device and BEOL interconnect above anarray device, the density of 3D memory devices can be increased.Moreover, by decoupling the peripheral device processing and the arraydevice processing, the thermal budget associated with processing thearray device is not limited by the peripheral device performancerequirement; similarly, the peripheral device performance is notimpacted by the array device processing. For example, the peripheraldevice and the array device can be separately fabricated on differentsubstrates so that certain high-temperature processes for fabricatingthe array device will not adversely affect the fabrication of theperipheral device (e.g., avoid excess diffusion of the dopants, controlthe doping concentration and/or thickness of ion implantation, etc.).

In some embodiments, a NAND memory device includes a substrate, aplurality of NAND strings on the substrate, one or more peripheraldevices above the plurality of NAND strings, a single crystallinesilicon layer above the one or more peripheral devices, and one or morefirst interconnect layers between the one or more peripheral devices andthe plurality of NAND strings.

In some embodiments, a 3D memory device includes a substrate, a memorystring extending vertically on the substrate, a peripheral device abovethe memory string, a semiconductor layer above the peripheral device,and a first interconnect layer. The peripheral device is at a firstsurface of the semiconductor layer. The first interconnect layer is on asecond surface of the first substrate.

In some embodiments, a 3D memory device includes a substrate, analternating conductor/dielectric stack on the substrate, a peripheraldevice above the alternating conductor/dielectric stack, and a pluralityof memory strings extending vertically through the alternatingconductor/dielectric stack. Each of the plurality of memory stringsincludes a semiconductor channel extending vertically through thealternating conductor/dielectric stack, a tunneling layer between thealternating conductor/dielectric stack and the semiconductor channel, astorage layer between the tunneling layer and the alternatingconductor/dielectric stack, and an epitaxial plug at a lower end of thememory string and in contact with the substrate.

In some embodiments, a NAND memory device includes a first semiconductorstructure, a second semiconductor structure, and a bonding interfacebetween the first semiconductor structure and the second semiconductorstructure. The first semiconductor structure includes a first substrate,a plurality of conductor/dielectric layer pairs on the first substrate,a plurality of NAND strings extending vertically through the pluralityof conductor/dielectric layer pairs, and a first interconnect layerincluding a first conductor layer at a surface of the first interconnectlayer. The second semiconductor structure includes a thinned secondsubstrate, one or more peripheral devices below the thinned secondsubstrate, and a second interconnect layer including a second conductorlayer at a surface of the second interconnect layer. The first conductorlayer contacts the second conductor layer at the bonding interface.

In some embodiments, a method for forming a NAND memory device isdisclosed. A plurality of NAND strings are formed on a second substrate.One or more peripheral devices are formed on a second substrate. The oneor more peripheral devices are positioned above the plurality of NANDstrings. The second substrate is above the plurality of NAND strings.The plurality of NAND strings and the one or more peripheral devices arejoined. The first second is thinned so that the thinned second substrateserves as a single crystalline silicon layer above the plurality of NANDstrings.

In some embodiments, a method for forming a 3D memory device isdisclosed. An alternating conductor/dielectric stack and a plurality ofmemory strings extending vertically through the alternatingconductor/dielectric stack are formed on a first substrate. A firstinterconnect layer is formed above the memory strings on the firstsubstrate. A peripheral device is formed on a second substrate. A secondinterconnect layer is formed above the peripheral device on the secondsubstrate. The first substrate and the second substrate are bonded, sothat the first interconnect layer is below and in contact with thesecond interconnect layer.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the present disclosure that others can, byapplying knowledge within the skill of the art, readily modify and/oradapt for various applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A three-dimensional (3D) memory device,comprising: a substrate; a plurality of NAND strings, wherein a firstsurface of the plurality of NAND strings opposes a second surface of theplurality of NAND strings, and the second surface of the plurality ofNAND strings is in contact with a first surface of the substrate; one ormore first interconnect layers, wherein a first surface of the one ormore first interconnect layers opposes a second surface of the one ormore first interconnect layers, and the second surface of the one ormore first interconnect layers is in contact with the first surface ofthe plurality of NAND strings; one or more peripheral devices, wherein afirst surface of the one or more peripheral devices opposes a secondsurface of the one or more peripheral devices, and the second surface ofthe one or more peripheral devices is in contact with the first surfaceof the one or more first interconnect layers; and a single crystallinesilicon layer, wherein a first surface of the single crystalline siliconlayer opposes a second surface of the single crystalline silicon layer,and the second surface of the single crystalline silicon layer is incontact with the first surface of the one or more peripheral devices. 2.The 3D memory device of claim 1, wherein the one or more peripheraldevices comprise one or more MOSFET devices.
 3. The 3D memory device ofclaim 1, further comprising an alternating conductor/dielectric stack,wherein each of the plurality of NAND strings comprises: a semiconductorchannel extending vertically through the alternatingconductor/dielectric stack; a tunneling layer between the alternatingconductor/dielectric stack and the semiconductor channel; and a storagelayer between the tunneling layer and the alternatingconductor/dielectric stack.
 4. The 3D memory device of claim 3, furthercomprising a first contact, wherein the first contact extends verticallythrough the alternating conductor/dielectric stack and comprises a lowerend in contact with the substrate.
 5. The 3D memory device of claim 1,further comprising a second interconnect layer in contact with the firstsurface of the single crystalline silicon layer, wherein the secondinterconnect layer comprises one or more layers of conductor layersformed in one or more dielectric layers.
 6. The 3D memory device ofclaim 1, wherein a NAND string of the plurality of NAND stringscomprises a first NAND string in contact with a second NAND string. 7.The 3D memory device of claim 6, wherein the NAND string and the anotherNAND string are electrically connected by a conductor.
 8. The 3D memorydevice of claim 1, further comprising a through silicon contact, whereinthe through silicon contact extends vertically through the singlecrystalline silicon layer, and wherein the through silicon contactelectrically connects with an interconnect layer of the one or morefirst interconnect layers on one end of the through silicon contact. 9.The 3D memory device of claim 1, wherein the single crystalline siliconlayer comprises a doped region and an isolation region.
 10. The 3Dmemory device of claim 1, wherein each of the plurality of NAND stringscomprises an epitaxial plug at a lower end of the each of the pluralityof NAND strings.
 11. The 3D memory device of claim 10, wherein theepitaxial plugs of the plurality of NAND strings contact a doped regionin the substrate.
 12. The 3D memory device of claim 10, wherein thesecond surface of the plurality of NAND strings comprise surfaces of theepitaxial plugs.
 13. The 3D memory device of claim 1, further comprisinga plurality of contacts, wherein each contact of the plurality ofcontacts is in contact with the first surface of the plurality of NANDstrings.